Polycarbonate and vinyl copolymer resin blend compositions can provide improved processability while maintaining high notched impact strength. Such resin blend compositions should also have good flame retardancy as well as high mechanical strength when used in the production of heat-emitting large-size injection molding products such as computer housings, office supplies, and the like. A halogen-containing flame retardant and an antimony-containing compound can be added to the compositions to impart good flame retardancy.
However, halogen-containing compounds can emit toxic gases generated during combustion. Accordingly, halogen-free resin compositions are used widely.
Phosphate ester-based flame retardants can be used as alternatives to halogen-based flame retardants. U.S. Pat. Nos. 4,692,488 and 5,061,745 are directed to a resin composition comprising aromatic polycarbonate, acrylonitrile-butadiene-styrene graft copolymer, thermoplastic copolymer and monomeric phosphate ester compound.
However, resin compositions including a monomeric phosphate ester compound as a flame retardant can have very poor heat resistance. Further such compositions can exhibit a so called “juicing phenomenon” during molding processes as a result of the flame retardant volatilizing and forming a laminate on the surface of molding product.
The molecular weight of the phosphoric acid ester can be increased to address the juicing problem. The molecular weight of the phosphoric acid ester can be increased by introducing a substitute group to a monomeric phosphate ester compound or using an oligomeric phosphate ester compound.
U.S. Pat. No. 5,206,404 is directed to a composition having stability against acid and hydrolysis by use of alkyl substituted aryl phosphate compound. Further, Japanese Patent Application Laid Open No. 59-202,240 is directed to a process of preparing an oligomeric phosphate ester compound and states that such compounds can be used as a flame retardant in polyamide or polycarbonate.
U.S. Pat. No. 5,204,394 is directed to a flame retardant resin composition comprising an aromatic polycarbonate resin, a styrene-containing copolymer or a graft copolymer, and oligomeric phosphate as flame retardant.
Although the resin composition can improve the juicing phenomenon and heat resistance, the flame retardancy exhibited by the composition can be inferior to that of a resin composition including a monomeric phosphate ester as a flame retardant Accordingly, to maintain good flame retardancy, the resin composition should contain more flame retardant than a resin composition containing a monophosphorous ester as a flame retardant.
U.S. Pat. No. 5,672,645 is directed to a PC/ABS resin composition containing an aromatic polycarbonate, a vinyl copolymer, a graft copolymer, a combination of a monophosphate ester and an oligomeric phosphate ester as flame retardants, and a fluorinated polyolefin, stated to have improved stress cracking resistance.
However, the resin composition still shows juicing phenomenon due to the monomeric phosphate ester compound. Further, the flame retardation ability of the resin composition is lowered due to the oligomeric phosphate ester.